The molecular biology of the glial component of the tripartite synapse has been woefully neglected. It's clear that the interactions of the post-synaptic and pre-synaptic sites of neurons balance with those of the astrocyte to produce a dynamic functional synapse. We propose to extend our previous work on neuronal dendrites to determine the capacity of astrocytic processes to locally control mRNA movement and protein translation. These studies will be divided into two specific aims with the first Specific Aim devoted to characterization of the mRNA expression profile in astrocytic processes and the associated cell soma. This will be accomplished using the single cell aRNA nucleic acid amplification procedure coupled with micro- and macro-array analysis. The second Specific Aim will assess the ability of neuronal stimulation to modulate translation of mRNAs in astrocytic processes. These experiments will utilize primary cultures of mouse astrocytes as vehicles for the transfection of mRNAs that upon translation give rise to detectable proteins. Astrocytic processes will be mechanically microdissected and various mRNAs transfected followed by fluorescent and immunodetection of protein locally translated from transfected mRNAs. Subsequent experiments will use intact astrocytes that have been transfected with caged rnRNA that inhibits the mRNA translation. Upon in vivo laser uncaging the mRNA can be translated at the site of uncaging. Such experiments in combination with siRNA knock-down of selective gene expression will also permit an analysis of the functional significance of astrocytic process synthesized proteins. At the end of this granting period we will have determined the complement of mRNAs that are localized to astrocytes and astrocytic processes. Further we will have determined whether astrocytic processes can translate these localized mRNAs as well as the spatiotemporal aspects of translation in this subcellular region. Finally using RNA transfection methodologies we will have determined whether neuronal activity modulates astrocytic process mRNA translation and using novel caged mRNAs, in concert with siRNA knock-down experiments, determined whether astrocytic translation of mRNAs can modulate synaptic activity.